This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-197659, filed Jul. 12, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an optical time domain reflectometer (to be referred to as xe2x80x9cOTDRxe2x80x9d hereinafter) and particularly relates to an optical pulse test system or OTDR making various measurements such as measurements of the loss, fault and the like of optical fIbers by applying an optical pulse from a light source onto a plurality of optical fibers which are connected with a connector or fusion-connecting them at predetermined intervals and by converting a reflected light (back scattering light, Fresnel reflected light) returned from the measurement target optical fibers following the incidence of this optical pulse into an electric signal to thereby process the resultant electric signal.
In an optical communication system employing optical fibers, a plurality of optical fibers are connected with a connector or fusion-connected at predetermined intervals to thereby form one transmission line.
When providing the above-stated transmission line, an OTDR for making various measurements by applying an optical pulse onto the optical fibers of the transmission line to be tested and signal-processing a reflected light accompanying the incidence of this optical pulse is employed.
FIG. 5 is a block diagram showing the schematic constitution of a conventional OTDR employed for the measurements of this type.
As shown in FIG. 5, this OTDR includes a timing generation section 11, a light emission section (light source) 12, an optical coupler 13, a light reception section 14, an amplifier 15, an A/D converter section 16, an adder circuit section 17 and an arithmetic operation control section 18 which serve as an OTDR measurement section 1a as a whole, as well as a display section 19 connected to the OTDR measurement section 1a. 
In this OTDR, an optical pulse emitted from the light emission section 12 driven by a signal from the timing generation section 11 is incident on measurement target optical fibers W through the optical coupler 13.
Following the incidence of the optical pulse, a reflected light reflected and returned from the measurement target optical fibers W is received by the light reception section 14 through the optical coupler 13, amplified with a predetermined amplification factor by the amplifier 15 and introduced to the A/D converter section 16.
In the A/D converter section 16, after the output of the amplifier 15 is sampled in a predetermined sampling cycle, each of the sampled data is supplied to the adder circuit section 17.
The adder circuit section 17 adds together the sampled data for a predetermined time and averages the data.
Each of the averaged data is supplied to the arithmetic operation control section 18.
The arithmetic operation control section 18 conducts arithmetic operation on various measurements based on the respective averaged data. The operation results are displayed as numeric value data and waveform data by the display section 19.
Meanwhile, if a transmission line is tested by employing the above-stated OTDR and multiple optical fibers are employed, various measurements are conducted to the respective optical fibers. The defective optical fiber, if any, is retested.
If all of the measurement result for the optical fibers are proven to be normal, a test is conducted on the entire optical fibers by continuous measurements.
The continuous measurements means repeatedly measuring optical fibers connected to the OTDR while switching over the optical fibers one after another under the same conditions without changing basic settings, or continuously measuring one optical fiber while switching over the wavelengths of an optical pulse incident on one optical fiber one after another.
The other change items include a distance range.
Furthermore, in evaluating whether a transmission line is defective or non-defective, splice loss and return loss at connected portions, unit length loss at intervals of the optical fibers, the total loss and a total return loss of an optical fiber from a tip end to a terminal end thereof are measured.
With the conventional OTDR, however, the data obtained by the continuous measurements on a cite where the transmission line is provided is only stored in an external storage medium such as a floppy disk. An evaluation processing for the transmission line cannot be conducted on a measurement cite based on the data.
Due to this, it is disadvantageously required that after the data thus stored are brought back from the measurement site and analyzed and the transmission line is evaluated, the transmission line evaluated as defective is measured again on the site.
As can be seen, the conventional OTDR cannot conduct an evaluation operation for the transmission line on the site based on the measurement data obtained on the site and the conventional OTDR has, therefore, disadvantageously lower working efficiency.
In the drawing of the display screen of a conventional OTDR when selecting various types of items of the OTDR disclosed by U.S. Pat. No. 5,801,953, nothing is disclosed about conducting an evaluation operation to a transmission line on a measurement site based on measurement data obtained on the site.
The present invention has been made in view of the above-stated disadvantages. It is, therefore, an object of the present invention to provide an optical time domain reflectometer capable of displaying a list of various measurement data measured in continuous measurements in units of files and improving the efficiency of an operator""s evaluation operation for a transmission line on a measurement site.
To obtain the above object, according to one aspect of the present invention, there is provided an optical time domain reflectometer for receiving a return light of an optical pulse incident on a measurement target optical fiber formed out of a plurality of optical fibers coupled in series and for measuring splice loss, return loss and unit length loss of the measurement target optical fiber, comprising:
a maximum value detector receiving the return light and detecting a maximum value due to an absolute value for the splice loss, and maximum values for the return loss and the unit length loss, of the measurement target optical fiber, respectively; and
a display unit displaying the maximum value due to the absolute value for the splice loss and the maximum values for the return loss and the unit length loss according to items of the splice loss, the return loss and the unit length loss, respectively, based on output from the maximum value detector.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from. the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.